The Californium-252 plasma desorption mass spectrometer puts unusual and stringent demands on the data system that controls the spectrometer and acquires and processes its data output. Realtime performance and the ability to access very large data arrays in main memory are key considerations. After delays necessitated by hardware design problems, software upgrades, and facilities renovations, both the spectrometer and a data system design modeled after one in use at Texas A & M University have been installed and are now functional. This instrument now provides NIH the capabilities of mass analysis for compounds that have proven difficult or impossible to analyze by other mass spectrometric means. It also extends the range of mass analysis to compounds with molecular weights in excess of 5000.